The present invention relates to an electrochemical power generator and, more particularly, to an electrochemical power generator wherein a plurality of unit cells, each having an anode of a grooved (or ribbed) porous substrate carrying a catalyst layer thereon, and a plurality of grooved (or ribbed) solid interconnectors are alternately stacked.
An electrochemical power generator, where an anodic oxidation of a gas such as hydrogen which tends to be oxidized and a cathodic reaction of a gas such as oxygen are performed to generate DC power by Gibb's free energy, generally has a structure where a plurality of unit cells are stacked up together. In stacking up the unit cells, electrical connections between the unit cells must be maintained, and at the same time a gas passage must also be provided to supply a reaction gas to the unit cells and to remove a reaction product therefrom.
In order to satisfy the above requirements, an electrochemical power generator is known in which interconnectors, each comprising a grooved conductive carbon plate of a high density are sandwiched between adjacent unit cells. In the power generator of this type, a number of parallel grooves are formed on the two surfaces of the carbon plate which constitutes the interconnector. The grooves on one surface are substantially perpendicular to those on the other surface. The grooves on each surface thus constitute a gas passage. In order to stack the plurality of unit cells with the interconnectors interposed therebetween, one surface of an interconnector is brought into contact with the cathode (or anode) of a unit cell, and the other surface thereof is brought into contact with the anode (or cathode) of the next unit cell. The reaction gas is supplied to the unit cells through the grooves of the interconnectors, and the reaction product is carried out therethrough. The unit cell is generally formed such that a thin porous carbon plate as a cathode is adhered to one surface of a chemical-resistant, heat-resistant and antioxidant matrix layer impregnated with an electrolyte solution consisting of a concentrated sulfuric acid solution or a concentrated phosphoric acid solution, and a thin porous carbon plate as an anode is adhered to the other surface of the matrix layer. The cathode and anode of the unit cell are catalyzed by a catalyst such as platinum to activate the electrochemical reaction and are waterproofed by polytetrafluoroethylene or the like. The electromotive force of the unit cell of this type is 1 V at best. Therefore, several tens or hundreds of unit cells must be stacked together to obtain a practical power generator.
In order to maintain a high activity over a long period of time in the electrochemical power generator of the type described above, the reaction gas must be sufficiently supplied to the unit cells and the reaction product must be quickly removed. Furthermore, the unit cells which constitute the power generating section must be firmly secured to each other. It is important to assemble the unit cells so as to have a minumum internal electrical resistance in order to increase the heat rate of the power generator. For this purpose, the ohmic loss of the matrix layer and the contact resistance loss between the interconnector and the electrode must be minimized. In this case, since the ohmic loss of the matrix layer is greatly changed in accordance with the amount of electrolyte solution impregnated in the matrix layer, there is a constant requirement over time for a sufficient amount of the electrolyte solution between the anode and the cathode. Furthermore, in order to firmly fix adjacent unit cells through the interconnector so as to minimize the resistance loss between adjacent units, the interconnector must be brought into tight contact with the adjacent unit cells.
However, in the conventional electrochemical power generator, the anode and the cathode are respectively made of thin porous carbon plates, and the interconnector is made of a very hard material having a density of about 1.8. When adjacent unit cells are pressed together sandwiching the interconnector therebetween, the unit cells are themselves compressed by the interconnectors. In the worst case, the unit cells are damaged. Further, the electrolyte solution is contained only in the matrix layer since the electrodes are very thin. Therefore, a sufficient amount of electrolyte solution cannot be contained in the unit cell, thus shortening the service life of the power generator.
In order to eliminate the above drawbacks, the following power generator is proposed. In this power generator, both the anode and cathode comprise a thick porous carbon plate in which grooves constituting a gas passage are formed on one surface thereof, and a catalyst layer is formed on the other surface. Furthermore, an interconnector comprises a thin conductive plate. According to the power generator of this type, since the anode and the cathode are made of thick porous carbon plates, respectively, they may not be damaged even if they are compressed. Furthermore, the electrolyte solution may also be impregnated in the anode and the cathode as well in the matrix layer. However, in the power generator of this type, the resistance loss is great since the anode and the cathode are thick. A gas may leak from the edge portions of the anode and the cathode, and air can hardly be dispersed, thus lowering utilization of the air.